Marine: fishy facts

Do whales have belly buttons? How many teeth does a haddock have? Are there any fish that eat people?

These are just some of the questions that you'll find answers to.

  • Do fish sleep? Yes, they do. But they don't have eyelids.
  • Some fish like sharks don't posses an air bladder to help keep them afloat and must either swim continually or rest on the bottom.
  • An ichthyologist is a person who studies fish.
  • Why are fish slimy? Fish secrete a type of mucus from their skin. This slime coating is important because it provides protection against parasites and diseases, covers wounds to prevent infection and helps fish move through the water faster. Some species release toxins in their slime which ward off attacking creatures while others use their slime to feed their young.
  • How do fish breathe? Some fish have lungs and breathe air, but most breathe through gills. Gills are made up of thin sheets of tissue richly supplied with blood vessels. As water passes over them dissolved oxygen is absorbed into the blood and waste products such as carbon dioxide pass out into the water. The gills are protected by a large bony plate called an operculum.
  • How can you tell how old a fish is? Scientists use ear growth rings, called an otiliths, to tell how old a fish is.

  • In the developing world, 60% of the people obtain more than 30% of their protein supply from fish.
  • Fishing is moving into deeper waters where fish grow and reproduce more slowly. Some species like orange roughy can live to 100 - 150 years, and this age structure needs to be taken into account when setting sustainable fishery yields.
  • The UK-hosted Continuous Plankton Recorder survey is the world's longest-running and most extensive large-scale biodiversity monitoring programme. It started in 1931, and now covers the North Atlantic and North Pacific and parts of the Southern Ocean and Arctic Ocean. More about monitoring...
  • UK researchers now routinely use ocean circulation models to predict where microscopic plants will flourish (phytoplankton blooms). Such organisms draw-down carbon and support most other life in the sea; they can also be toxic and their decay may reduce oxygen levels, affecting fish.
  • The UK has the largest wave, tidal and offshore wind resources in Europe. Such energy sources could potentially provide 15-20% of UK electricity. More about Marine Renewables energy...

  • Tracking devices have been developed by UK researchers to follow the movements of fish, sea mammals and turtles. For seals, mobile phone technology is used to transmit data back to researchers.
  • The greatest genetic resource on Earth is in the sea. More than 100,000 species of microbes have been found at one site in the English Channel, and there is more DNA in a bucket of seawater than in the human body.
  • Medical equipment developed to count blood cells has been adapted by UK scientists to sort and classify marine microbes.
  • Why are fish called fish? The word “Fish” covers lots of different types of thing, actually but most precisely describes any animal with a skull, and in most cases a backbone, that has gills throughout life and whose limbs, if any, are in the shape of fins.
  • What did fish evolve from? The earliest organisms that can be classified as fish were soft-bodied  organisms that first appeared about 1.7 million years ago. Fish may have evolved from a creature similar to a coral-like Sea squirt

  • How long can fish survive out of water? Some fish can survive for up to several days and can breathe air or just absorb it through their skin

  • How do the fish suck the oxygen out of the water? How can fish swim under the water? How does a fish hold its breath? Most fish have filters in their gills that help them take the oxygen out of water

  • Why do fish stay together? Why do fish swim together in a shoal? What's the largest size of shoal? Only some fish stay together, the likes of our herring and mackerel.  They do this in part for protection.

  • Can fish float? If they can, would they float in the Dead sea? Most fish rise and sink in the water by using their air bladder. The only float on the surface when they die and the air bladder stops working. And no, there are no fish in the Dead sea

  • How long can fish swim for without taking a break?  Can they stop for a break? Do fish have to keep moving to stay alive? Do fish ever stop swimming?     Fish don’t always swim - sometimes, when they’re tired, they hitch a ride on the current to save energy

  • If a fish swims backwards will it die? Although most fish don't usually swim backwards, there are some kinds that can if they want to

  • Do fish have feelings and emotions? Yes, they can get stressed and sad

  • What is the difference between a pet fish and a fish in the sea? Not a lot really, except the pet fish does not risk getting eaten

  • Are there any fish called aliens? We often refer to Alien species, which just means fish that are not normally found in Scottish waters. So if you found a parrot fish in the Clyde this would be considered an alien species

  • Do any fish sting people? Yes, some can like the Weever fish and Scorpion fish

  • When fish sleep do they wake up in a different place? They can do, but because they’re not usually on their own, they don’t get lost                    

Fish and Food

  • Are all fish edible?  Can you eat all fish raw? Yes, most are but some species of fish, notably the puffer fugu used for sushi, and some kinds of shellfish, can poison you if they're not prepared properly
  • Do fish have allergies? Probably and research is going on into this at the moment
  • How much food does a fish eat? It depends on the size of the fish.  The largest fish - which is actually the whale shark - eats lots and lots, including plankton, fish, other sharks, dolphins, whales, seals, sealions, turtles and otters.
  • Do fish eat each other? What fish eat plankton? Do they eat dead fish? Yes, different fish eat different things including plankton and other fish
  • What does a blobfish eat? Blobfish eat invertebrates like crabs and sea pens
  • What does an Angler fish eat? They eat small fish and shrimp and they can also feed on small squids, turtles, crustaceans, arrow worms and even sea birds
  • Can fish be physically sick? Yes, they can
  • Do fish need the same type of vitamins as we do and then we get them when we eat the fish? Yes they do and that is why they eat each other, but remember the fish get it from the copepod oil in the first place
  • Why is only the tail of the monkfish eaten? It has the tastiest amount of usable white meat, a bit like a chicken's breast
  • Is it true that in Japan they eat puffer fish which are deadly?  Yes. Certain internal organs, such as liver, and sometimes the skin, are highly toxic to most animals when eaten
  • What is the maximum amount a fish can eat in a day? It depends on the size of the fish!  The biggest fish - the whale shark - eats lots and lots of plankton but other fish eat lots too, like other sharks, dolphins, whales, seals, sealions, turtles and otters
  • Are there fish that will eat people? Yes - Pirhanas
  • Is it true that when plankton grows on a fish that other fish come along and it the plankton? Yes.  Smaller fish come along and clean the bigger fish by eating the plankton
  • Why do fish eat skin off human feet? Some fish will eat anything put in front of them!

  • What is the nick name for cod? Green
  • Do all fish have food sacks? The food sacks that many fish have is when they are very young and it is how they get their food when they are very young


  • Do other fish use FARTS (Fast Repetitive Ticks)?  We do not know for sure, underwater sound is extremely complex and our technology has still to catch up. Much more research need to find out these things
  • Why do they FART to go faster? To escape from danger
  • What is the most popular fish that is caught by fishing boats? Haddock
  • Do any fish have poison parts?  Yes - some puffer fish do
  • Do fish sleep? Yes, but they don't have eyelids
  • How long do trout sleep for?     As long as they need, depending on what they have been doing
  • Can all fish communicate with each other? We don’t know this also requires much more research
  • What is the loudest fish? It's called a croaker
  • Do all fish understand each other? We don’t know - it needs more research

Fish Biology 

  • The heart of a blue whale is the size of a mini cooper car
  • Why are flat fish flat?   They just are, really, but it helps them hide from prey . Some flatfish are also able to change their colour to match the background
  • Why are salmon pink inside? Most salmon aren't really pink - they are generally orange to red, although there are some examples of white-fleshed wild salmon
  • What percentage of a fish's size is made up of brain? Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth (0.06%) the brain mass of a similarly sized bird or mammal
  • Can fish smell? Do fish have noses? Most fish have highly developed senses - Nearly all daylight fish have colour vision - that is at least as good as a human - and fantastic senses of taste and smell
  • How deep can fish go? Any single type of fish has a relatively narrow depth range.  However, different fish live at dufferent depths.  Fish at 7,700 m are very deep water fish and they cannot live in much shallower water

  • What does a dog fish look like? A dog fish does not look like a dog, but it is a fairly long and sleek animal
  • How do you know if a fish is a boy or a girl? The sex of a fish ranges from easy to nearly impossible to find out, but can involve differing colours, bumps on the head and size
  • Do clown fish have teeth? Why do clown fish have so many babies? Yes, they have teeth and they’re just lucky - they can lay 100s of eggs
  • Do fish look after their babies? They usually try to protect them from predators and try to take them to areas were there is something to eat
  • Are gills like slits in their body?  Yes, but they don’t hurt and are very important
  • Do fish have eye lashes? No
  • Do all fish have blue eyes? No - you get different colours
  • Do any fish have legs?   Technically, none. They have fins, not legs. However, there are some fish who have modified fins which look like, and can even act like, legs. Such as Lungfish, Frogfish and Gurnards
  • Do any fish have hair? Nope - although some dolphins have a few hairs
  • Can fish cry? No - they don't have any tear ducts
  • How many teeth do haddock have? It can depend, but lots
  • Are different species of fish attracted to each other? Can different species of fish mate? No - not normally
  • How do they fish know when it is bedtime? They just sleep when they need to
  • Do mummy fish feed their babies? No , but they try to make sure that they hatch out where there is something for them to eat
  • Why do catfish have lots of babies? All fish have as many babies as possible to make sure that more survive to be adult fish
  • What's the biggest cold blooded fish? The Whale shark
  • Do any fish have a different colour of blood? Nope - they all have red blood
  • Is the bottom of the sea full of fish droppings? Do fish go to the toilet? Yes, they do and it just falls in to the water and gets mixed up with everything else
  • Why is the male angler fish so small? Nobody really knows!

Body Beautiful 

  • Why are some deep water fish are multi-coloured? How do fish change colour? This is because of chemicals in their skin
  • Can fish get sunburn?    Yes, fish can get sunburned, but it is unusual unless there is something about their environment that does not allow them to seek deeper water or some kind of shelter
  • Why do gold fish turn white in the dark? Goldfish change color all the time and unless it happens very fast, like over night then its nothing to worry about. Sunlight helps keep color but if you don't have a pond and don't want to build one color enhancing food may help. The genes of the fish tell it what color to be though, so if its genes are telling it to turn white then there is nothing you can do about it.
  • How do fish protect themselves from predators? Some change colour, some can swim very fast and some hide!
  • Do fish get harmed when they are used in films? No. There are very strict rules that have to be followed if you want to work with fish or any animals
  • How do fish disguise themselves? They change their skins colour or they hide!

Fishy Technology  

  • How high can flying fish fly? Flying fish fly through the air a few feet above the water's surface. Their flights are typically around 50 meters (160 ft)
  • Which kind of fish can live in the coldest temperatures? Antartic ice fish, which have antifreeze in their blood, live permantley at -1 degee. Brr!
  • Do fish have ''night vision''?  Sort of. Fish vision shows adaptation to their visual environment, for example deep sea fishes have eyes suited to the dark environment
  • How does the angler fish produce the light on top of his head? How does the fish use its light bulb? It uses a chemical reaction to make the light work and then uses it to help see food
  • Why do fish at the bottom of the sea look different to those at the top of the sea? It can be because of many things, including how the sunlight reacts with the chemicals in their body
  • How can certain fish can live at the bottom of the ocean and we can't get down there? Fish are made in a very clever way which means that the pressure of being underwater doesn't affect them
  • Do fish know where they are? Yes - they have a kind of in-built system, like Satnav in your car/a GPS computer system to tell them
  • Do fish help the environment? What would happen if there were no fish? The sea would very quickly become a desert and live on land would even more quickly become not very nice
  • Is it true that a fish surrounds itself by its snot to protect itself? Yes - parrotfish produce a mucus "tent" that completely covers them
  • Do any fish live near underwater volcanoes? Yes - some species have learned to survive where it's very hot. Things like tubeworms, bacteria, crabs, mussels and clams live there
  • How does the sonar that has a fish has work?  By using sound in water it bounces off the air in the swim bladder of the fish and makes an echo
  • What fish live in the coldest part of the world? Goldfish, koi, and other members of the carp family are able to survive in cold water temperatureS. Lake trout, arctic char, and arctic grayling can also survive in very cold water
  • How do fish that lie in deep parts of the sea see things? How can fish see underwater as it hurts our eyes? Because their eyes are different to ours and they have learned to adjust to see things that we can't
  • Can fish get caught in seaweed? No, not really
  •  How many spikes do puffer fish have?  How big can pufferfish puff out? They have lots of spines and it gets much fatter when it puffs - at least twice the size!
  • Why do some fish glow in the deeper dark water? Because they have special chemicals in their skin
  • Why do most fish live at the bottom of the sea? They don't - they are fish living at lots of different depths of the sea
  • Why do fish have tails? Because it helps them swim and it's just the way the have evolved
  • Why did the Megladon become extinct? It might have been because the seas got colder or the sea level dropped or that food ran out
  • How many species of fish are known to live in the midnight zone? We really don’t know much more research is needed every year more and more deepwater species are being described
  • Is the Loch Ness Monster really a big fish? No one really knows for sure, but it is possible.
  • An ichthyologist is a person who studies fish.
  • Why are fish slimy? Fish secrete a type of mucus from their skin. This slime coating is important because it provides protection against parasites and diseases, covers wounds to prevent infection and helps fish move through the water faster. Some species release toxins in their slime which ward off attacking creatures while others use their slime to feed their young.



Marine Directorate
Mailpoint 11
1B South
Victoria Quay

Telephone: 0300 244 4000


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